Analysis of powder and dispersion. Development of formulations and pigment testing
causes of differences
The reason for differences in the handling of a bulk material is often the different flow properties. We measure the flow properties of your bulk material.
Strongly cohesive bulk solids have transport, conveying, dosing and storage properties that are difficult to handle. These macroscopic bulk solid properties depend on moisture, particle shape, surface properties, particle size distribution and cohesiveness.
The aim is to work with extended characterization properties that differentiate between the use cases.
test methods
Cohesion test using a powder rheometer
The property of the powder particles sticking together and forming agglomerates can be referred to as cohesion property. The rotation geometry cuts through the powder column. Compression effects are minimized here. As it is twisted out, the powder is lifted and the force the powder exerts on the bottom of the container is recorded. A more cohesive powder will form agglomerates and adhere to the geometry of rotation. This results in a reduction in the force directed at the container bottom when twisting out of a cohesive powder. A negative course of forces is recorded and the areas under the curves are evaluated.
Measured parameters
Fluidity in the form of a cohesion index.
Fig. 2: Evaluation of collected cohesion measurement data
Cracking test using a powder rheometer
By driving the rotational geometry onto the powder surface, a normal load is applied to the
Powder column applied and compacts the sample. At a preset force, the process
stopped, registering the height of the powder cake at that point. Then the
Rotational geometry driven out of the powder again.
The cycle of this powder compression process is repeated four more times. The fifth time
the rotation geometry completely penetrates the powder cake down to the bottom of the sample vessel
after the preset target force has been reached. The clumping tendency is from height and
Strength of the powder cake calculated (Fig.2).
Measured parameters
• Column to cake height ratio
• Energy to destroy the powder cake
• Firmness of the powder cake
Fig. 2: Evaluation of collected cohesion measurement data
Carr's Indices (ASTM D-6393)
The flowability of bulk materials is correlated with the compaction properties of the powder by determining the so-called Hausner Index and Carr Index using standardized bulk and bulk density determinations. The powder flowability is evaluated using the FFI flowability index, which is determined from a table after the Carr experiments have been carried out.
This type of flowability assessment is intended for cohesionless to moderately cohesive bulk solids.
norms
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EN ISO 787-11 Determination of tapped density
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DIN ISO 697 Determination of bulk density
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ASTM D-6393 Determination of Carr's Indices
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D-6773: Standard Shear Test Method for Bulk Solids
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ASTM D-7891 - 15 Standard Test Method
